Oh dear, Ray, you're going over very old ground here and stuff that's been mulled over on Mudcat for seemingly centuries. In fact it's a Mudcat tradition. As I've said many times whenever these definitions crop up the words mean different things to different people. Even such a small circle as the British Folk Scene uses this expression in two different ways rather loosely. Most of us who have been around for a while have been used to using the expression to describe those people like you have mentioned above, Walter Pardon, Harry Cox, Jim Copper and all those people recorded by Sharp, Grainger, Kidson, Gardiner etc. but as it has become more used to describe simply people like ourselves who sing traditional songs we have become more inclined to use the expression 'source singer'. As you won't find these expressions in a dictionary there is little point in arguing the toss.